The present invention relates to horizontal belt vacuum filters and more particularly to a fluid aircushion and fluid film air bearing arrangement for supporting the outer undersurfaces of the transport belt used in such filters to provide a more evenly balanced supporting force across the belt thus distributing the frictional forces acting thereon and reducing uneven belt wear.
Horizontal belt vacuum filters have been successfully used for filtration and washing applications in the chemical, food and mineral processing industries. Such filters of various constructions are available commercially but many problems have been experienced with regard to continuous reliable service and ready and easy maintenance in the adverse operating environments encountered in chemical and mineral processing operations.
For example, a basic problem in these filters is the supporting of the horizontal transport belt in a manner to minimize the friction thereon and the resulting wear during its continuous movement while filter is in operation.
An example of a typical prior art filter, and one on which the present invention is intended to improve, is one in which the outer ends of the transport belt are supported by respective fluid film bearings produced by means of air boxes containing rectangular pressurized chambers and having a series of pressure releasing holes across their flat upper surfaces. The pressurized air from the interiors of the air boxes escapes through the holes in the flat upper surfaces and forms fluid layers or air slides on which the undersurface of the transport belt rides.
With this arrangement, if the top surfaces of the air boxes are not completely flat, air escapes at the outer edges so that the contact pressure on the undersurface of the belt is uneven and concentrates on those top areas which are highest tending to stop all air flow in those areas and thereby allowing the air pressure to dissipate through the randomly occurring lower top areas. This uneven pressure results in a significant increase in frictional drag on the underside of the transport belt. While this system has generally operated in a satisfactory manner, it has been found that with extended use the uneven pressure gradient acting on the underside of the belt results in some areas of the belt experiencing excessive wear in the region or regions where the box is irregular either transversely or longitudinally.
The present invention is intended to overcome the problem presented by uneven support pressure acting on the underside of the belt that can result in uneven belt wear by providing an improved air box construction which produces an evenly balanced support pressure and thus promotes long belt life.
For an understanding of the principles involved in fluid film bearings and a review of the prior art, reference may be had to the text "Fluid Film Lubrication" by William A. Gross, et al. published by Wiley Interscience, 1980, John Wiley & Sons, New York.